Replacement Instead of Discontinuation of Bacillus Calmette-Guérin Instillation in Non-Muscle-Invasive Bladder Cancer

Simple Summary Most patients with intermediate- and high-risk non-muscle-invasive bladder cancer (NMIBC) fail to complete bacillus Calmette-Guérin (BCG) instillation due to toxicity or shortage. Our retrospective study aimed to assess the efficacy of intravesical chemotherapy replacement at the time of BCG interruption. We confirmed the chemotherapy replacement group had a better three-year bladder recurrence-free survival (RFS) than the BCG discontinuation group. Chemotherapy replacement is then a helpful strategy in patients with NMIBC facing BCG treatment stoppage. Abstract Background: To evaluate the efficacy of intravesical chemotherapy replacement in patients with intermediate- and high-risk non-muscle-invasive bladder cancer (NMIBC), who underwent bacillus Calmette-Guérin (BCG) instillation but discontinued due to global shortages or toxicity of BCG. Methods: This retrospective study included patients with intermediate- and high-risk NMIBC who received BCG intravesical instillation. Those who discontinued the treatment were divided into the pure BCG group and chemotherapy replacement group. Comparisons between these groups were performed. The primary endpoint was bladder recurrence-free survival (RFS). Results: A total of 480 patients were included. Baseline characteristics were similar between groups, but the total instillation times were higher in the chemotherapy replacement group than in the pure BCG group (n = 14.9 vs. 10.5). The chemotherapy replacement group had a better three-year RFS (p = 0.022). On multivariate analysis, the pure BCG group had significantly increased all-time and 3-year recurrences (hazard ratio 2.015 and 2.148) compared to the chemotherapy replacement group. Conclusions: Chemotherapy replacement has a better three-year RFS than no instillation in patients with intermediate- and high-risk NMIBC who received BCG instillation but facing treatment stoppage.


Introduction
Bladder cancer accounts for approximately 573,278 new cases diagnosed per year and is the tenth most common cancer worldwide.
The tumor stage of bladder cancer is assigned by the depth of the bladder wall invasion. Tumors with muscle layer invasion or beyond are considered muscle-invasive bladder cancer (MIBC). It could be further divided into non-metastatic or metastatic disease, accounting for approximately 4% of the newly diagnosed bladder cancers. In contrast, the cancers confined to the urothelium and the lamina propria layer are called non-muscleinvasive bladder cancer (NMIBC), accounting for approximately 75% of newly diagnosed bladder cancer [2,3].
In treating NMIBC, transurethral resection of bladder tumor (TUR-BT) is the first step that improves clinical and pathological features such as tumor size, number, stage, and histology grade [3]. Based on these variables, patients can be stratified into low, intermediate, and high risk. The prognosis of each risk group is different, thus requiring different treatment recommendations [4]. The European Association of Urology (EAU) guidelines suggest only a single installation of intravesical chemotherapy in low-risk groups, while further induction and maintenance of adjuvant intravesical agents for intermediate and high-risk groups [5]. Among the adjuvant treatments, intravesical bacillus Calmette-Guérin (BCG) immunotherapy is considered superior to the other agents in preventing recurrence and progression [5]. However, only 16% of patients tolerate the whole BCG treatment course due to significant toxicity [6].
Besides the toxicity of BCG that hinders the continuity of BCG, another added problem is BCG shortage. In the past decade, several events, such as BCG plant closures and manufacturer withdrawal have reduced BCG production and led to a supply-demand mismatch [7]. Strategies including a change of BCG schedule or adopting intravesical chemotherapy are discussed to cope with the BCG instillation discontinuation.
In this retrospective study, we compared the outcome of patients with NMIBC who received BCG instillation after suffering from discontinuation due to side effects or shortage, and those who received initial BCG instillation and discontinued then shifted to intravesical chemotherapy. We aimed to investigate whether intravesical chemotherapy replacement is helpful in patients who discontinued BCG either due to intolerant side effects or BCG shortage.

Patient Population
We conducted a retrospective study including patients diagnosed with bladder cancer between January 2005 and December 2020 in a single tertiary medical center. The medical charts of these patients were reviewed. Only those diagnosed with NMIBC administered intravesical BCG instillation therapy after TUR-BT were enrolled. Patients without contraindications such as bleeding with clots or bladder perforation received immediate single instillation (SI) of intravesical chemotherapy within 24 h after the TUR-BT. We classified these patients based on EAU NMIBC prognostic factor risk groups [8]. The low-risk group was excluded since an SI was considered treatment complete in this group, and EAU guidelines suggested no further intravesical instillation was needed. Patients with previous urothelial carcinoma history (including bladder or upper urinary tract) or other malignancy history were eligible. This study was approved by the Institutional Review Board (IRB) of Chang Gung Memorial Hospital. The IRB of Chang Gung Memorial Hospital waived the requirement for patient consent to review their medical records due to the study's retrospective nature. The data collection confidentiality agreement fulfilled the requirements of the Declaration of Helsinki.

Risk Group Classification
Based on the EAU guideline and the 2004/2016 WHO histological grading system [8], we defined low risk as a primary, solitary, Ta, papillary urothelial neoplasm of low malignant potential (PUNLMP) or low grade (LG) tumor with a size smaller than 3 cm and no carcinoma in situ (CIS). On the other hand, the high-risk group was defined as any of the following: T1, high grade (HG), or CIS. Ta LG tumors with multiple, recurrent, and large (>3 cm) features all presented were regarded as high-risk. Finally, tumors that could not be classified into the low or high-risk category were defined as intermediate risk.

Data Collection
Patients' general characteristics were collected: gender, age, body height, body weight, body mass index (BMI), smoking habit, comorbidity, and cancer history. We also identified tumor-related parameters, including tumor stage, histology, pathological grade, tumor size, tumor number, and risk group. Intravesical instillation data were also recorded, including the number of BCG, the alternative chemotherapy instillation if it existed, and the number of total intravesical instillations (IVI).

Endpoints
Local recurrence of bladder cancer was set as the primary endpoint, while patients were followed for recurrence-free survival until the final analysis. Recurrence-free survival (RFS) was defined as the period from diagnosis to the time of bladder recurrence. In the absence of confirmation of bladder recurrence, RFS time was censored at the last date at which the patient was known to be recurrence-free. Secondary endpoints were progression to muscle-invasive disease, progression-free survival, the event of death, and overall survival. Moreover, the reason for BCG discontinuation and the appearance of side effects, including local or systemic, were identified.

Follow Up
All patients received regular follow-ups with cystoscopy every three months in the first two years, then every six months for another two years, and annually.

Intravesical Instillation Dosage and Protocol
The protocol of BCG instillation consisted of six-weekly instillation as an induction course and one-year maintenance course (three weekly instillations at months 3, 6, and 12) for the intermediate-risk group. As for the high-risk group, the maintenance course would extend to three years, with an additional three weekly instillations at months 18, 24, 30, and 36. The dose of BCG was 81 mg during each instillation. The BCG strains were BCG-TICE (OncoTICE ® , MSD, Rahway, NJ, USA). The chemotherapy agents used in the alternative intravesical instillation were epirubicin (50 mg of each dose) and mitomycin C (40 mg of each dose). Only a single agent was used during each instillation.

Statistical Analysis
We analyzed the correlation of each parameter with Pearson Chi-square, Fisher's exact test, and the independent-T test. Recurrence-free, progression-free, and overall survival were analyzed with the Kaplan-Meier survival test. We regarded p-values less than 0.05 as significant. Univariate and multivariate analyses were performed using log-rank tests and Cox proportional hazard regression. Significant variables (p < 0.05) or neared significance (p < 0.2) in univariate analysis were included in the multivariate analysis. All statistical analyses were performed using IBM SPSS Statistics 26.00 software (IBM Corp., Armonk, NY, USA).

Results
A total of 3351 patients with bladder cancer were initially assessed. After excluding MIBC and those without BCG instillation records, 497 patients with NMIBC and receiving BCG intravesical instillations were enrolled, with only 17 patients completing the whole course of BCG instillation. Among the 480 patients who had BCG instillation interruption, 421 completed the induction course but dropped out during the maintenance course, and others failed to complete the induction course. A total of 90 patients received alternate chemotherapy instillation after BCG discontinuation. The enrollment flowchart is illustrated in Figure 1.
MIBC and those without BCG instillation records, 497 patients with NMIBC and receiving BCG intravesical instillations were enrolled, with only 17 patients completing the whole course of BCG instillation. Among the 480 patients who had BCG instillation interruption, 421 completed the induction course but dropped out during the maintenance course, and others failed to complete the induction course. A total of 90 patients received alternate chemotherapy instillation after BCG discontinuation. The enrollment flowchart is illustrated in Figure 1. Among the enrolled patients, the male-to-female ratio was 3.40, and the mean age at diagnosis was 66.7 years. Ninety-two patients (18.5%) had a history of bladder cancer. Of all included patients, 40.4% and 53.9% had stage Ta and T1, respectively, while only 5.6% had pure Tis stage. Histological high-grade tumors accounted for 75.9%. Four hundred thirteen patients (83.1%) were categorized in the high-risk group. The mean follow-up period was 70.8 ± 46.0 months. The detailed characteristics of the patients, such as BMI, comorbidity and cancer history, and other tumor parameters, are listed in Table 1.  Among the enrolled patients, the male-to-female ratio was 3.40, and the mean age at diagnosis was 66.7 years. Ninety-two patients (18.5%) had a history of bladder cancer. Of all included patients, 40.4% and 53.9% had stage Ta and T1, respectively, while only 5.6% had pure Tis stage. Histological high-grade tumors accounted for 75.9%. Four hundred thirteen patients (83.1%) were categorized in the high-risk group. The mean follow-up period was 70.8 ± 46.0 months. The detailed characteristics of the patients, such as BMI, comorbidity and cancer history, and other tumor parameters, are listed in Table 1. Comparison analysis was performed between the groups using intravesical chemotherapy as an alternative after BCG discontinuation (short as [BCG + Chemo]) and the pure BCG group (short as [BCG only]). The general characteristics and tumor-related parameters were analyzed, with no statistical difference in most parameters except in instillation counts ( Table 2). The [BCG only] patients received more BCG instillation than [BCG + Chemo] group (10.5 vs. 7.3, p < 0.001), but the latter had statistically more total IVI counts (10.5 vs. 14.9, p < 0.001). group showed a significantly higher survival rate than the [BCG only] group (log-rank test: p = 0.022). The progression-free survival (PFS) and overall survival (OS) between these two groups were analyzed, and no statistical difference was found (log-rank test: p = 0.275 and 0.075, respectively). The Kaplan-Meier survival plots are illustrated in Figure 2. stillation; Cis = Carcinoma in situ; BCG = Bacillus Calmette-Guérin; SD = Standard Deviation.
During a median follow-up duration of 59.3 months (range: 2.6-227.1 months), the all-time bladder recurrence-free survival (RFS) revealed a better trend in the [BCG + Chemo] group than the [BCG only] group. However, it did not reach the statistical difference (log-rank test: p = 0.072). As we focused on the three-year RFS, the [BCG + Chemo] group showed a significantly higher survival rate than the [BCG only] group (log-rank test: p = 0.022). The progression-free survival (PFS) and overall survival (OS) between these two groups were analyzed, and no statistical difference was found (log-rank test: p = 0.275 and 0.075, respectively). The Kaplan-Meier survival plots are illustrated in Figure  2. Univariate and multivariate analyses using the Cox regression method were performed to evaluate the effect of various parameters on recurrence events. Both all-time recurrence and three-year recurrence share similar independent factors: diabetes mellitus, Univariate and multivariate analyses using the Cox regression method were performed to evaluate the effect of various parameters on recurrence events. Both all-time recurrence and three-year recurrence share similar independent factors: diabetes mellitus, chronic kidney disease, history of bladder cancer, tumor stage and number, risk group category, and instillation methods. The [BCG only] method was significantly associated with increased all-time recurrence (HR = 2.015; 95% CI 1.169-3.474) and three-year recurrence (HR = 2.148; 95% CI 1.208-3.819) relative to the [BCG + Chemo] method (Table 3). Among the population of BCG interruption, BCG shortage accounted for 21.3% of the reasons for discontinuation, while 21.0% were due to the side effects. About 42.8% of the stoppage was due to individual requirements without objective toxicity events. Side effects could be further divided into systemic (30.7%) and local effects (69.3%), with the former including fever and malaise, and the latter consisting of lower urinary tract symptoms (LUTS) and urinary tract infection (UTI). The details are illustrated in Figure 3.

Discussion
The current consensus on the maintenance protocol of BCG instillations was based on several randomized trials and meta-analyses [9][10][11][12][13], which is superior to BCG induction alone or chemotherapy instillation in reducing recurrences of bladder cancer. BCG toxicity has been well recognized during the long instillation protocol and has gained

Discussion
The current consensus on the maintenance protocol of BCG instillations was based on several randomized trials and meta-analyses [9][10][11][12][13], which is superior to BCG induction alone or chemotherapy instillation in reducing recurrences of bladder cancer. BCG toxicity has been well recognized during the long instillation protocol and has gained more attention. In the BCG toxicity report of an EORTC randomized study [14], the proportion of local and systemic side effects is about 2:1, similar to our study results. Further trials were conducted to achieve less toxicity, without affecting patient prognosis [15].
The EORTC 30962 trial was designed with randomization of its study population by dosage (one-third dose or full dose) and duration of maintenance (one or three years) [16]. The results showed no statistical differences in toxicity among these treatment groups. Neither reducing the dose nor shortening the maintenance duration would lead to less toxicity. The NIMBUS trial showed a reduced frequency of BCG schedule of nine instillations within twelve months, which was inferior to the standard protocol (15 instillations) in recurrence-free intervals, and therefore being early halted by the EAU Research Foundation [6]. Another modified BCG maintenance regimen, as one BCG instillation every three months following induction therapy, was evaluated in the CUETO 98013 trial, which showed no benefit in reducing recurrence and progression rates than induction therapy alone [17].
In addition to a marked side effect of BCG, another reason for treatment stoppage is BCG shortage. Between 2013 and 2016, the closure of BCG production factories led to a worldwide shortage of BCG. A retrospective study evaluated the impact of the shortage by comparing the bladder cancer recurrence rate before and after the shortage. A higher recurrence rate was found in the group with instillation treatment during the BCG shortage period [18]. Due to the COVID-19 epidemic, the role of BCG as a nonspecific immune stimulant was re-emphasized, increasing the global demand. This growing use and need for BCG led to another episode of worldwide shortage and was declared by American Urological Association (AUA) announcement [19].
Besides changing the regimen of BCG instillation, using chemotherapy as an intravesical instillation agent was acceptable in NMIBC treatment. Adjuvant chemotherapy instillation significantly reduced the recurrence rate than TUR-BT alone [20]. Comparison between BCG and chemotherapy instillation has been well studied, and chemotherapy appeared inferior to BCG maintenance therapy in terms of recurrence prevention with fewer side effects [13,21,22]. Some studies have reported device-assisted intravesical chemotherapy such as microwave-induced chemohyperthermia or electromotive methods to amplify the cytotoxic effects of chemotherapy on bladder tumor cells, and the results were promising. One RCT using MMC with microwave-induced hyperthermia method presented a significantly higher 24-month RFS than BCG in the intermediate-and high-risk papillary NMIBC [23]. However, these methods encountered challenges in administration due to the need for expensive machines and trained employees [23][24][25][26].
This study has focused on the population who received initial BCG instillation but faced stoppage either due to BCG shortage or intolerance to toxicity. Shifting to intravesical chemotherapy instillation during BCG discontinuation seemed feasible, and our results support this hypothesis. We found that chemotherapy as an alternative would have significantly higher three-year recurrence-free survival than stopping further instillation. Moreover, shifting to chemotherapy instillation is an independent protecting factor for three-year and all-time recurrence. Most importantly, this strategy does not need an extra device and could reduce recurrence without increasing side effects. This easily applicable feature makes our findings worth more emphasis.
One limitation of this study was the retrospective study design, which might affect the evidence level. Despite equivalent results between subgroups analysis, selection bias should also be considered as there might be implicit factors that make people more willing to receive different instillation agents than stop treatment. Another limitation is the small target population size, with only 90 patients receiving BCG and alternative chemotherapy instillation. This might be due to the multiple selections during inclusion, as the cohort should have BCG instillation first with an incomplete treatment course, then have chemotherapy instillation as an alternative. Finally, issues such as comparing the [BCG + Chemo] group versus the BCG protocol complete group or cancer-specific survival between different instillation strategies remain unclear. Further sample size expansion or prospective study would lead to a more precise comprehension of these issues.

Conclusions
For patients with intermediate-and high-risk NMIBC who received BCG instillation and have faced treatment stoppage, subsequent replacement with chemotherapy agents has a better three-year RFS. Our strategy could still be practiced simply and efficiently in reducing the bladder recurrence rate. Informed Consent Statement: Patient consent was waived due to the retrospective study design through the review of medical records only. The research involves no more than minimal risk to the subjects. The waiver or alteration will not adversely affect the rights and welfare of the issues. The study could only practically be carried out with the waiver or alteration. Whenever appropriate, the subjects will be provided with additional pertinent information after participation. Data Availability Statement: Data available on request due to restrictions e.g., privacy or ethical. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to their containing information that could compromise the privacy of research participants.

Conflicts of Interest:
The authors declare no conflict of interest.